It has to do with a gramma switch. Normally electricity is bulit with a circut and its the building of a circuit thats assur.
A gramma switch is already on and it has to do with changing the directions of the electrons so you are only indirectly affecting the electricity.
Truthfully anyone could really do this, but its been disallowed for healthy people, but the Poseks have allowed this for people who really need the wheelchairs or for elevators (The kind in a house where you sit) or in a shul to reach the other floors